The talk addresses wave motion in an unbounded fluid-loaded elastic sandwich plate composed by two identical isotropic skin plies and an isotropic core ply in a general three-dimensional problem formulation. Several alternative theories for stationary dynamics of such a plate are suggested, including a formulation in the framework of a theory of elasticity applied for the core ply. In the first instance, a fluid loading at the both sides of a plate is considered and 'in-phase' and 'anti-phase' wave motions (with respect to transverse deflections of skins) are analysed independently upon each other. Dispersion curves are compared and it is shown that the simplified models are capable to give a complete and accurate description of all propagating waves in not too high frequency range, which is sufficient in practical engineering. The role of sound emission into the acoustic medium in wave propagation phenomena is studied. Furthermore the analysis is extended to take into account for the 'symmetry-breaking' effects, e.g., a static pre-stress of one of skin plies and a fluid loading at one side of the sandwich plate. The standard perturbation technique is applied to analyse an interaction between dispersion curves in these cases.
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